How can I render an edge only mesh as solid lines?
Note: This answer is for 2.79 only. For 2.8+ you will have to look at some of the other answers.



The simplest way to render an object that has no faces is to change the material type in the internal renderer to a 'Wire' material:



The mesh on the left, when rendered, looks like the image on the right:



I also changed it to be 'Shadeless' in the shading panel of the material so that it wouldn't be affected by shadows and would be lit equally.